ABSTRACT
Recombinant mammalian cells are used increasingly for studies of gene function and expression, and for large-scale production of specific proteins. Chinese hamster ovary (CHO) cells, in particular, are routinely used for protein production in pharmaceutical applications. A unique feature associated with CHO-DUKX cells is the possibility of selecting and establishing cell subpopulations and clonal cell lines which, upon treatment with methotrexate, have amplified transfected expression vector sequences to high copy numbers within their chromosomes. Southern DNA blot analysis provides little information about subpopulation heterogeneity and rearrangement of amplified sequences and no information on chromosomal location and number of integration sites. The loci of integration and the degree of amplification of recombinant sequences in cells are thought to vary between individual clones and thus may be unique descriptors for identification of recombinant cell lines. The resulting population of cells containing defined, often more modestly amplified sequences, was genetically stable and showed consistent protein production rates over extended culture periods.
